It is known that high power pulse lasers comprise an oscillator followed by a series of amplifiers, a light pulse generated by the oscillator being amplified by the series of amplifiers to provide a high intensity output light pulse. Such a pulse has many industrial applications such as welding, object detection, guidance, laser-controlled fusion experiments and plasma heating.
The various amplifying media are pumped by light excitation or by electronic excitation before the light pulse generated by the oscillator passes through them for amplification. In carbon dioxide gas lasers, of the transverse excitation type for example, an electronic discharge inverses the populations of the vibration-rotation levels of the carbon dioxide gas molecules before the passage of the light pulse generated by the oscillator.
A major problem connected with the presence of successive high gain amplifiers is the power loss due to the phenomenon of superradience, i.e. the amplification of the photon flux generated by spontaneous emission in the time interval between excitation of the amplifying medium and the passage of a light pulse therethrough. Indeed, the photons released by spontaneous emission in the pumped medium are amplified by the amplifying media; this creates a pencil of light which is considerably amplified on its passage through a second amplifying medium with the effect of depopulating the laser transition levels in the second medium and rendering them no longer useable for amplifying the laser pulse generated by the oscillator; further this unwanted light can itself be a hinderance in some applications.